Such lock and key systems of the kind known from the above mentioned US patents (Bo Widén) provide a high level of security as compared to conventional systems without rotatable tumblers and pivoting fingers thereon. A great number of code combinations can be achieved, and the locks are very difficult to pick or manipulate. The tumblers are only partially visible in the key slot, and their correct elevational and pivotal code positions are hidden from inspection through the key slot. Therefore, the particular code positions cannot be determined from just observing the key slot or even by sensing the finger positions with a tool.
The side code portions of the wave-like guiding surface (sometimes also called side bittings) of the key blade of the previously known key are each constituted by a concavity surface portion having two upwardly sloping surface portions adjoining smoothly on each longitudinal side thereof. It has also been suggested, in a pending international application PCT/SE04/001312 (WINLOC AG), to locate some of the side code portions at an uppermost vertical code level where the guiding surface is substantially flat.
The possible side code portions associated with a particular side locking tumbler for a code structure involve different combinations of predetermined vertical levels and a number of longitudinal positions in relation to the side locking tumbler. In a typical system, which has been in commercial use for many years, the number of side tumblers is five (in addition to six centrally located tumblers cooperating with an upper edge of the key blade). The side material region, where the wave-like guiding surface or side bitting is cut at the side of the key blade, has a relatively small height (perpendicularly to the longitudinal direction of the key blade), such as about 2.0 mm (about 0.080 inches). Therefore, only a limited number of vertical levels can be accommodated while clearly differentiating between different codes, in particular two such levels, 0.60 mm (0.024 inches) and 1.20 mm (0.048 inches), respectively, calculated from the bottom edge of the key blade.
Such differentiated levels pertain to a particular pivotal position of the finger of the associated side locking tumbler. In the embodiments used hitherto, there are two vertical levels corresponding to each pivotal end position of the finger (at a pivotal angle of +15° and −15°), two further levels corresponding to an intermediate pivotal position (at a pivotal angle of 0°), each being slightly higher than the first-mentioned levels, viz. 0.90 mm (0.036 inches) and 1.50 mm (0.060 inches), respectively, and the above-mentioned uppermost level constituting another code position, possibly irrespective of the specific pivotal position of the tumbler finger.
Accordingly, for each side locking tumbler in the example above, there are seven possible codes, viz.                two code portions at different vertical levels corresponding to a pivotal end position at +15°,        two code portions at different vertical levels corresponding to a pivotal end position at −15°,        two code portions at different, slightly higher vertical levels corresponding to an intermediate pivotal position,        and a further code portion at the uppermost vertical level,making a total of seven possible code portions for each side locking tumbler or a total of 7×7×7×7×7=16807 different combinations.        
Of course, it would be desirable to increase this high number of combinations even further. However, the dimensions of the keys are greatly standardized and also adapted to existing manufacturing facilities. In practice, there is virtually no possibility to pack the vertical levels closer together, or to use more than three different pivotal positions. Therefore, it appears necessary to find some other way to increase the number of code combinations.